use character-base ranges when looking for classes

packages/tailwindcss-language-service/src/completionProvider.ts

@@ -306,7 +306,7 @@ function provideClassAttributeCompletions(
   context?: CompletionContext
 ): CompletionList {
   let str = document.getText({
-    start: { line: Math.max(position.line - 10, 0), character: 0 },
+    start: document.positionAt(Math.max(0, document.offsetAt(position) - 500)),
     end: position,
   })
 

packages/tailwindcss-language-service/src/util/find.ts

@@ -360,9 +360,10 @@ export async function findClassNameAtPosition(
   position: Position
 ): Promise<DocumentClassName> {
   let classNames = []
-  const searchRange = {
-    start: { line: Math.max(position.line - 10, 0), character: 0 },
-    end: { line: position.line + 10, character: 0 },
+  const positionOffset = doc.offsetAt(position)
+  const searchRange: Range = {
+    start: doc.positionAt(Math.max(0, positionOffset - 500)),
+    end: doc.positionAt(positionOffset + 500),
   }
 
   if (isCssContext(state, doc, position)) {